Typical features of Axial Spondyloarthritis on plain radiographs
The radiographic changes of axSpA are predominantly seen in the axial skeleton (sacroiliac, apophyseal, discovertebral, and costovertebral) as well as at sites of enthesopathy (“whiskering” of the iliac crest, greater tuberosities of the humerus, ischial tuberosities, femoral trochanters, calcaneus, and vertebral spinous processes). Sacroiliitis is usually bilateral and symmetric. Initially, it involves the synovial-lined lower two-thirds of the sacroiliac joint.
The earliest radiographic change is minimal erosion of the iliac side of the sacroiliac joint, where the cartilage is thinner and has clefts, or sclerosis (Grade 2). Progression of the erosive process may result in moderate to significant erosions, sclerosis, widening, narrowing, or partial ankylosis of the sacroiliac joint space (Grade 3), eventually followed by complete bony ankylosis or fusion of the joint (Grade 4). In cases of early sacroiliitis where plain radiographs may be normal or equivocal, a noncontrast MRI may be ordered
Inflammatory disease of the spine involves the insertion of the annulus fibrosis to the corners of the vertebral bodies, resulting in initial “shiny corners” (Romanus lesion) followed by “squaring” of the vertebral bodies ( Fig. 34.4 ). Gradual ossification of the outer layers of the annulus fibrosis (Sharpey’s fibers) forms intervertebral bony bridges called syndesmophytes. Fusion of the apophyseal joints and calcification of the spinal ligaments along with bilateral syndesmophyte formation can result in complete fusion of the vertebral column, giving the appearance of a “bamboo” spine. Calcification of the supraspinous ligament can end caudally in a tapering point (dagger sign). Some patients develop an inflammatory destructive spondylodiscitis (Andersson lesion) that can mimic infection.
